Aluminum is conventionally produced in aluminum smelters by electrolysis using the Hall-Héroult process. To this end, an electrolytic cell is provided comprising a pot shell and a lining of refractory material. The electrolytic cell also comprises cathode blocks arranged at the bottom of the pot shell, covered by conductive bars designed to collect the electrolysis current in order to route it to the next electrolytic cell. The electrolytic cell also comprises at least one anode block suspended from an anode support, such as a cross-piece and partially immersed in an electrolytic bath, above the cathode blocks. A layer of liquid aluminum, covering the cathode blocks, is formed as the reaction proceeds. Current flow takes place from the anode support to the cathode via the anode block and the electrolytic bath at a temperature of about 970° C. in which the alumina is dissolved. This electrolysis current can reach several hundreds of thousands of amperes. The anode block is then suspended by an intermediate member, capable of carrying the high current, of withstanding these very high temperatures and of supporting the weight of the anode, such as a stub made of steel.
In such a device, a very large heat flow is formed between the carbon anode and the anode support. This heat transfer is the source of major and detrimental energy loss in the electrolysis process.
It was observed that locally reducing the cross section of the stub made it possible to obtain a significant temperature drop: from 650° C. to 320° C. for a reduction in section over a stub length of about 10 cm. In the solid section of the stub, the extraction of heat to the anode support is primarily through conduction, and reducing the cross section of the stub greatly limits heat transfer by conduction. In this configuration, the stub may be formed of two portions having different cross-sections which can be machined or formed from separate welded elements to reduce the thermal energy loss by conduction. However, this section reduction reduces electrical conductance and therefore increases power consumption. Moreover, this solution has a significant financial cost because it requires at least a portion to be machined from an available stub in the general shape of a standard cylinder. This machining step is also time-consuming and contributes to a substantial loss of material.
It is known from patent publication U.S. Pat. No. 6,977,031 to place a thermally insulating disc between the bottom wall of the stub and the bottom of a sleeve serving to fix the stub into a recess in the anode. This thermally insulating disk arranged in the bottom of the recess allows better control of the heat flow path, which must, in the arrangement of U.S. Pat. No. 6,977,031, pass through the sides of the recess, the vertical walls of the sleeve and then the stub in order to improve the removal of heat from the anode to the anode support. The result obtained with the arrangement of U.S. Pat. No. 6,977,031 is therefore opposite to that intended, i.e. to reduce heat loss from the anode to the anode support.